Mutations in the fused in
sarcoma/translocated in
liposarcoma (FUS/TLS) gene have been associated with
amyotrophic lateral sclerosis (ALS). FUS-positive neuropathology is reported in a range of
neurodegenerative diseases, including ALS and fronto-temporal lobar degeneration with
ubiquitin-positive pathology (FTLDU). To examine
protein aggregation and cytotoxicity, we expressed
human FUS protein in yeast. Expression of either wild type or ALS-associated R524S or P525L mutant FUS in yeast cells led to formation of aggregates and cytotoxicity, with the two ALS mutants showing increased cytotoxicity. Therefore, yeast cells expressing
human FUS protein recapitulate key features of FUS-positive
neurodegenerative diseases. Interestingly, a significant fraction of FUS expressing yeast cells stained by
propidium iodide were without detectable
protein aggregates, suggesting that membrane impairment and cellular damage caused by FUS expression may occur before
protein aggregates become microscopically detectable and that aggregate formation might protect cells from FUS-mediated cytotoxicity. The N-terminus of FUS, containing the QGSY and G rich regions, is sufficient for the formation of aggregates but not cytotoxicity. The C-terminal domain, which contains a cluster of mutations, did not show aggregation or cytotoxicity. Similar to TDP-43 when expressed in yeast,
FUS protein has the intrinsic property of forming aggregates in the absence of other human
proteins. On the other hand, the aggregates formed by FUS are
thioflavin T-positive and resistant to 0.5%
sarkosyl, unlike TDP-43 when expressed in yeast cells. Furthermore, TDP-43 and FUS display distinct domain requirements in aggregate formation and cytotoxicity.